Niu et al. Journal of Orthopaedic Surgery and Research (2017) 12:106 DOI 10.1186/s13018-017-0615-y
RESEARCH ARTICLE
Open Access
Patella morphological alteration after patella instability in growing rabbits Jinghui Niu, Qi Qi, Yingzhen Niu, Conglei Dong, Zhenyue Dong, Peng Cui and Fei Wang*
Abstract Background: The shape of the patella has been considered to be a predisposing factor resulting in patellar instability, but the effects of abnormal patella position during its development are unclear. The present study evaluated patellar morphological changes after patella instability and evaluated the influence of patellar instability on the patella shape. Methods: Twenty rabbits that were 2 months old were included in the study. The left knee of each rabbit, defined as the experimental group (N = 20 knees/group), underwent a medial soft tissue restraint release. The right knee of each rabbit, defined as the control group (N = 20 knees/group), did not undergo any surgical procedures. A CT scan was performed on each knee before surgery and 6 months post-surgery to measure the transverse diameter, thickness, Wiberg index, and Wiberg angle for analysis of the patellar morphological changes. Cross-specimen examination was conducted to evaluate the differences between the experimental group and the control group. Results: The four indices remained the same between the two groups before surgery. However, 6 months after surgery, the mean transverse diameter of the patellae in the experimental group was significantly longer than that in the control group (P < 0.001), while the mean thickness in the experimental group was not significantly greater than that in the control group (P = 0.314), resulting in a flattened shape. The Wiberg indices were not significantly different between the two groups. However, the mean Wiberg angle was higher in the experimental group than in the control group (P < 0.001), which resulted in a flattened articular surface of the patella. Conclusion: The sectional shape and articular surface of the patella became more flattened after patella instability in this study, which indicates that patella dysplasia could be caused by patella instability. Clinically, early intervention for adolescent patients with patella instability is important. Keywords: Knee, Patella, Patella dislocation, Rabbits
Background The patellofemoral joint is formed by the articulation between the patella and the trochlear groove. The patella is the largest sesamoid bone in the body and sits distal to the muscle bulk of the quadriceps. Geometrically, the patella is shaped like an upside-down triangle [1]. The patella anatomy reveals a median crest traversing in the articular part of the patella, defining a medial and a lateral facet, and the shape-based classification has been proposed by Wibeeg [2]. The patella plays an essential role in knee functions. It acts as a biomechanical lever arm and improves the effective extension capacity of the * Correspondence: [email protected] Third Hospital of Hebei Medical University, No. 139 Ziqiang Road, Shijiazhuang City, Hebei State, China
quadriceps muscle by increasing the moment arm of the patellar tendon. Additionally, it prevents excessive friction between the quadriceps tendon and the femoral condyles [3]. The femoral trochlea consists of the lateral and medial facets of the femoral sulcus [1]. The lateral facet of the femoral trochlea prevents the patella from lateral subluxation and allows it to remain centred in the trochlea during normal knee function [3]. At full knee extension, the patella lies superior to the trochlear cartilage. As the knee flexes to 30°, the patella begins to articulate with the femoral trochlea. Between 30° and 90° of flexion, the inferior part of the patella initially engages with the trochlear, followed by the superior part. Beyond 120° of flexion, the contact area is reduced and only the small
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Niu et al. Journal of Orthopaedic Surgery and Research (2017) 12:106
odd facet remains in contact with the femur. The contact area is approximately 2.1 cm2 at 30° of flexion and increases to approximately 5.5 cm2 at 90° of flexion [4, 5]. In addition to the superior and inferior motion of the patella, it also tracks lateral-medial-lateral and tilts laterally during tibiofemoral extension to flexion. The patella translates medially 4 mm when it comes to engage with the trochlear groove and then translates to 7 mm laterally by 90° knee flexion. The patellar medial-lateral rotation is usually less than 3° [6]. Overall, the normal action of the patellofemoral joints is a very complex movement pattern, and the patella comes into contact and is restricted by the femoral trochlea during flexion and extension of the knee. The relationship between patella instability and trochlear groove morphology has been the topic of extensive research. Trochlear dysplasia has been described as a predisposing factor for patella dislocation [7]. A magnetic resonance imaging (MRI) study demonstrated that patients with instability of the patella exhibit a flatter distal trochlear groove compared to those without the instability [8]. The effect of the position of the patella on the development of the femoral trochlea has been studied and reported. Li et al. [9] and Wang et al. [10] found femoral trochlear dysplasia or flattening after patella instability in growing rabbits. Kaymaz et al. [11] demonstrated that the trochlea flattened after surgery with respect to the patella alta in growing rabbits. These studies indicate that femoral trochlea dysplasia could be caused by instability of the patella. Although the patella articulates with the femoral trochlea, studies on the correlation between patella morphology and patella instability are lacking. Although patella-shaped disorder is considered as a predisposing factor for patella instability [12], the effect of patella instability on patella morphology development has remained unclear. However, acetabular dysplasia has been proven to be caused by hip dislocation [13, 14]. Considering the similarities between the patellofemoral joint and the hip joint, it may be that patella dysplasia could be caused by patella instability. Based on the articulation of the patella and femoral trochlea and the similarities between the patellofemoral joint and the hip joint, we hypothesized that early patella instability might lead to morphological alterations in the patella during growth. The objectives of the present study were to elucidate the patellar morphology after instability of the patella in growing rabbits and to discuss the influence of patella instability on patella morphology.
Page 2 of 6
medical university), were divided into two groups. The left knees comprised the experimental group and were subjected to medial soft tissue restraints release. The right knees formed the control group, and no surgical interventions were performed. The dislocation procedure was as follows. (1) The rabbits were administered intravenous anaesthesia of ketamine hydrochloride and xylazine at a dosage of 20 and 5 mg/kg body weight, respectively. (2) The knees in the study group were shaved and disinfected by standard procedures. (3) A 3-cm incision was created on the knees in the study group, and the soft tissue was dissected to expose the medial retinaculum and medial side of the joint capsule. (4) A 3-cm longitudinal incision was made along the medial side of the patella to cut the medial retinaculum and joint capsule. Following the release of these structures, patellar instability was seen intraoperatively (Fig. 1). The patella dislocated (the femoral trochlear could be seen) when the knee was flexed, and it returned to the relatively normal position when the knee was extended. (5) After the operation, the incision was sutured, and post-anaesthetic recovery of the rabbit was allowed in an incubator. Caution was exercised to avoid damage to the articular cartilage. Ciprofloxacin (10 mg/kg, po) was administered 3 days after surgery for antibiotic prophylaxis. The rabbits were raised under the same conditions with water and food. Each animal was housed in an individual stainless steel (310 × 550 × 320 mm) cage, which was sufficiently large for normal activity. According to Masoud et al. [15], skeletal growth and maturation of rabbits is complete at 28 weeks of age. Therefore, all of the rabbits were followed until 6 months post-surgery, after which the animals were sacrificed by venous air embolism.
Measurements CT assessments
Computerized tomography (CT) scans were performed before surgery and 6 months post-surgery. All rabbits
Methods Study design and surgical procedures
The present study was approved by the local Animal Ethics Committee. Forty knees from 20 healthy, 2-month-old New Zealand white rabbits, weighing between 450 and 550 g (provided by the Animal Test Center of the local
Fig. 1 Medial retinaculum and joint capsule was cut
Niu et al. Journal of Orthopaedic Surgery and Research (2017) 12:106
were anaesthetized by the intravenous injection of ketamine hydrochloride and xylazine at a dosage of 20 and 5 mg/kg body weight, respectively, before CT scans were conducted. Six months post-surgery, patella instability was found in every knee in the experimental group after anaesthesia. CT images were captured in the axial plane, which is the optimal position to observe the articulation of the patellofemoral joint. The measurements were analysed by RadiAnt-DICOM software (Medixant Ltd., Poznan, Poland) in the CT machine, which provided an accuracy of 0.1° for angle and 0.01 mm for length (Fig. 2). The slice image with the widest diameter of the patella was used for the measurements in the transverse plane. Stäubli et al. [16] defined the length between the most medial edge (A) and the most lateral edge (B) of the patella as the transverse diameter (AB). The posterior patellar edge farthest from the baseline was defined as point D. The thickness of the patella was measured by the length of line CD vertical to the baseline. The insertion between line AB and line CD was defined as point E. The Wiberg index (length of BE/length of AB) was calculated, and the Wiberg angle (∠D) was measured as described by Fucentese et al. [17]. All measurements were recorded and averaged by three independent researchers who did not know the grouping. Cross observation
CT scans were performed 6 months post-surgery. Subsequently, the rabbits were sacrificed with air venous embolism, and the patellae were dissected and separated. Morphological differences were observed visually. Statistics
Statistical analysis was performed using the SPSS version 21.0 (SPSS, IL, USA). Student’s t test was used to evaluate the mean difference in the length of AB, the length of CD, and the volume of the Wiberg index and Wiberg
Page 3 of 6
angle between the control and experimental groups. A P value
RESEARCH ARTICLE
Open Access
Patella morphological alteration after patella instability in growing rabbits Jinghui Niu, Qi Qi, Yingzhen Niu, Conglei Dong, Zhenyue Dong, Peng Cui and Fei Wang*
Abstract Background: The shape of the patella has been considered to be a predisposing factor resulting in patellar instability, but the effects of abnormal patella position during its development are unclear. The present study evaluated patellar morphological changes after patella instability and evaluated the influence of patellar instability on the patella shape. Methods: Twenty rabbits that were 2 months old were included in the study. The left knee of each rabbit, defined as the experimental group (N = 20 knees/group), underwent a medial soft tissue restraint release. The right knee of each rabbit, defined as the control group (N = 20 knees/group), did not undergo any surgical procedures. A CT scan was performed on each knee before surgery and 6 months post-surgery to measure the transverse diameter, thickness, Wiberg index, and Wiberg angle for analysis of the patellar morphological changes. Cross-specimen examination was conducted to evaluate the differences between the experimental group and the control group. Results: The four indices remained the same between the two groups before surgery. However, 6 months after surgery, the mean transverse diameter of the patellae in the experimental group was significantly longer than that in the control group (P < 0.001), while the mean thickness in the experimental group was not significantly greater than that in the control group (P = 0.314), resulting in a flattened shape. The Wiberg indices were not significantly different between the two groups. However, the mean Wiberg angle was higher in the experimental group than in the control group (P < 0.001), which resulted in a flattened articular surface of the patella. Conclusion: The sectional shape and articular surface of the patella became more flattened after patella instability in this study, which indicates that patella dysplasia could be caused by patella instability. Clinically, early intervention for adolescent patients with patella instability is important. Keywords: Knee, Patella, Patella dislocation, Rabbits
Background The patellofemoral joint is formed by the articulation between the patella and the trochlear groove. The patella is the largest sesamoid bone in the body and sits distal to the muscle bulk of the quadriceps. Geometrically, the patella is shaped like an upside-down triangle [1]. The patella anatomy reveals a median crest traversing in the articular part of the patella, defining a medial and a lateral facet, and the shape-based classification has been proposed by Wibeeg [2]. The patella plays an essential role in knee functions. It acts as a biomechanical lever arm and improves the effective extension capacity of the * Correspondence: [email protected] Third Hospital of Hebei Medical University, No. 139 Ziqiang Road, Shijiazhuang City, Hebei State, China
quadriceps muscle by increasing the moment arm of the patellar tendon. Additionally, it prevents excessive friction between the quadriceps tendon and the femoral condyles [3]. The femoral trochlea consists of the lateral and medial facets of the femoral sulcus [1]. The lateral facet of the femoral trochlea prevents the patella from lateral subluxation and allows it to remain centred in the trochlea during normal knee function [3]. At full knee extension, the patella lies superior to the trochlear cartilage. As the knee flexes to 30°, the patella begins to articulate with the femoral trochlea. Between 30° and 90° of flexion, the inferior part of the patella initially engages with the trochlear, followed by the superior part. Beyond 120° of flexion, the contact area is reduced and only the small
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Niu et al. Journal of Orthopaedic Surgery and Research (2017) 12:106
odd facet remains in contact with the femur. The contact area is approximately 2.1 cm2 at 30° of flexion and increases to approximately 5.5 cm2 at 90° of flexion [4, 5]. In addition to the superior and inferior motion of the patella, it also tracks lateral-medial-lateral and tilts laterally during tibiofemoral extension to flexion. The patella translates medially 4 mm when it comes to engage with the trochlear groove and then translates to 7 mm laterally by 90° knee flexion. The patellar medial-lateral rotation is usually less than 3° [6]. Overall, the normal action of the patellofemoral joints is a very complex movement pattern, and the patella comes into contact and is restricted by the femoral trochlea during flexion and extension of the knee. The relationship between patella instability and trochlear groove morphology has been the topic of extensive research. Trochlear dysplasia has been described as a predisposing factor for patella dislocation [7]. A magnetic resonance imaging (MRI) study demonstrated that patients with instability of the patella exhibit a flatter distal trochlear groove compared to those without the instability [8]. The effect of the position of the patella on the development of the femoral trochlea has been studied and reported. Li et al. [9] and Wang et al. [10] found femoral trochlear dysplasia or flattening after patella instability in growing rabbits. Kaymaz et al. [11] demonstrated that the trochlea flattened after surgery with respect to the patella alta in growing rabbits. These studies indicate that femoral trochlea dysplasia could be caused by instability of the patella. Although the patella articulates with the femoral trochlea, studies on the correlation between patella morphology and patella instability are lacking. Although patella-shaped disorder is considered as a predisposing factor for patella instability [12], the effect of patella instability on patella morphology development has remained unclear. However, acetabular dysplasia has been proven to be caused by hip dislocation [13, 14]. Considering the similarities between the patellofemoral joint and the hip joint, it may be that patella dysplasia could be caused by patella instability. Based on the articulation of the patella and femoral trochlea and the similarities between the patellofemoral joint and the hip joint, we hypothesized that early patella instability might lead to morphological alterations in the patella during growth. The objectives of the present study were to elucidate the patellar morphology after instability of the patella in growing rabbits and to discuss the influence of patella instability on patella morphology.
Page 2 of 6
medical university), were divided into two groups. The left knees comprised the experimental group and were subjected to medial soft tissue restraints release. The right knees formed the control group, and no surgical interventions were performed. The dislocation procedure was as follows. (1) The rabbits were administered intravenous anaesthesia of ketamine hydrochloride and xylazine at a dosage of 20 and 5 mg/kg body weight, respectively. (2) The knees in the study group were shaved and disinfected by standard procedures. (3) A 3-cm incision was created on the knees in the study group, and the soft tissue was dissected to expose the medial retinaculum and medial side of the joint capsule. (4) A 3-cm longitudinal incision was made along the medial side of the patella to cut the medial retinaculum and joint capsule. Following the release of these structures, patellar instability was seen intraoperatively (Fig. 1). The patella dislocated (the femoral trochlear could be seen) when the knee was flexed, and it returned to the relatively normal position when the knee was extended. (5) After the operation, the incision was sutured, and post-anaesthetic recovery of the rabbit was allowed in an incubator. Caution was exercised to avoid damage to the articular cartilage. Ciprofloxacin (10 mg/kg, po) was administered 3 days after surgery for antibiotic prophylaxis. The rabbits were raised under the same conditions with water and food. Each animal was housed in an individual stainless steel (310 × 550 × 320 mm) cage, which was sufficiently large for normal activity. According to Masoud et al. [15], skeletal growth and maturation of rabbits is complete at 28 weeks of age. Therefore, all of the rabbits were followed until 6 months post-surgery, after which the animals were sacrificed by venous air embolism.
Measurements CT assessments
Computerized tomography (CT) scans were performed before surgery and 6 months post-surgery. All rabbits
Methods Study design and surgical procedures
The present study was approved by the local Animal Ethics Committee. Forty knees from 20 healthy, 2-month-old New Zealand white rabbits, weighing between 450 and 550 g (provided by the Animal Test Center of the local
Fig. 1 Medial retinaculum and joint capsule was cut
Niu et al. Journal of Orthopaedic Surgery and Research (2017) 12:106
were anaesthetized by the intravenous injection of ketamine hydrochloride and xylazine at a dosage of 20 and 5 mg/kg body weight, respectively, before CT scans were conducted. Six months post-surgery, patella instability was found in every knee in the experimental group after anaesthesia. CT images were captured in the axial plane, which is the optimal position to observe the articulation of the patellofemoral joint. The measurements were analysed by RadiAnt-DICOM software (Medixant Ltd., Poznan, Poland) in the CT machine, which provided an accuracy of 0.1° for angle and 0.01 mm for length (Fig. 2). The slice image with the widest diameter of the patella was used for the measurements in the transverse plane. Stäubli et al. [16] defined the length between the most medial edge (A) and the most lateral edge (B) of the patella as the transverse diameter (AB). The posterior patellar edge farthest from the baseline was defined as point D. The thickness of the patella was measured by the length of line CD vertical to the baseline. The insertion between line AB and line CD was defined as point E. The Wiberg index (length of BE/length of AB) was calculated, and the Wiberg angle (∠D) was measured as described by Fucentese et al. [17]. All measurements were recorded and averaged by three independent researchers who did not know the grouping. Cross observation
CT scans were performed 6 months post-surgery. Subsequently, the rabbits were sacrificed with air venous embolism, and the patellae were dissected and separated. Morphological differences were observed visually. Statistics
Statistical analysis was performed using the SPSS version 21.0 (SPSS, IL, USA). Student’s t test was used to evaluate the mean difference in the length of AB, the length of CD, and the volume of the Wiberg index and Wiberg
Page 3 of 6
angle between the control and experimental groups. A P value
